1. Field of the Invention
Very generally, the present invention relates to a method of forming a finishing welt for use in upholstery, such as in automobiles. More specifically, the welt is formed by extrusion and then embossed in two separate, sequential embossing operations to form a grained appearance on its exterior surface.
2. The Prior Art
Finishing welts made of plastic materials are now quite commonly used in automotive interiors to join the edges of two adjacent upholstery panels. Typically, such welts include a bead portion to provide a decorative appearance at the line of upholstery juncture and a flange to which the upholstery panels are sewn or otherwise attached. With the welts serving these functions, it is desirable that the bead be embossed with a grain appearance and that the flange be reinforced. Additionally, it is desirable to provide the welt bead with an inner reinforcement for extended durability.
Prior methods of making welts have experienced various undesirable shortcommings or disadvantages, which have been solved by the present invention.
For example, one prior method of embossing a welt included passing the welt bead simultaneously through two adjacent graining rollers. This method, while achieving the grained appearance, is undesirable because it forms a longitudinal non-grained rib on the welt bead at the line of contact between the two rollers.
A second prior art method includes passing the welt beneath one graining roller, which flattens and embosses approximately one half of the welt bead, but leaves the other half of the bead around the flange ungrained. Obviously, this method is undesirable from a decorative standpoint.
A third prior art method of forming a welt has been highly successful at providing a grained appearance over the entire welt bead, but includes several other manipulative steps which may be eliminated by the present invention. This third method is disclosed in U.S. Pat. No. 2,958,909 and includes the steps of (a) extruding a substantially flat plastic preform having a raised segment destined to become the welt bead, (b) embossing the raised preform portion by a roller to provide the grained appearance, (c) bending the preform into the configuration of the welt and then (d) fusing the two portions of the welt flange together.
A fourth method of making a finishing welt involves simply adhering the component parts by an adhesive. In this method, the outer layer of plastic material is formed in a sheet and then embossed on one side. Subsequently, the sheet is cut into segments, which are adhesively secured to a fabric scrim. Thereafter, the adhered scrim and plastic segments are wrapped around a plastic rod and adhered by adhesive in the desired shape. This method is undesirable from at least two aspects: First, the manipulative adhering steps are both time-consuming and costly. Second, the scrim formed by this method is somewhat easily disassembled into its component parts, by virtue of its being held together only by an adhesive.
Thus, the prior art methods of forming welts are incapable of forming an integral welt including a reinforcing rod and scrim, wherein the entire welt bead is embossed and the plastic material is integrally bonded to and through the scrim in the welt flange.
The present invention overcomes these problems by extruding polyvinyl chloride material over a composite preform in a cross head extruder and then sequentially embossing the two opposed sides of the welt bead.
Of course, other prior art has previously suggested the formation of reinforced articles by extruding plastic material over one or more preforms, examples of such prior art being U.S. Pat. No. 3,697,209, 3,487,149, 3,899,384, 3,544,669, 2,422,281, and 3,375,550. However, none of these Patents suggest the overall method, apparatus, or product of this invention.